This invention relates to a collar stud assembly and more particularly to a collar stud assembly suitable for use in a plastic boss having a bore therein to facilitate the joining of the plastic boss with another threaded member. In the automotive industry use is made of thermoset plastic resins for numerous large moldings which are assembled to structural members or other components by means of bosses molded integral with these moldings and into which double-ended collar fasteners are threaded.
Typically, the double-ended fasteners have a single shank with a first thread suitable for threading into plastic on one end of the shank, a second thread adapted to threadingly engage a nut or other threaded member on the other end and a collar disposed between the first and second threads and limiting the threading movement of the first and second threads. Although a properly sized bore is provided in the boss, the relatively brittle plastic boss often cracks, with resultant loss of holding power. Moreover the tendency for cracking is further aggravated by imperfections which often occur at the extremity of the boss due to the manner in which the parts are molded. Consequently, considerable loss is incurred in scrapped parts, production is curtailed and quality is questionable. Furthermore, there are times when the boss appears satisfactory at the time of assembly, but then fails in the field because of stress-cracking due to service conditions.
In U.S. Pat. No. 3,521,349 to Gehring, description is made of a method of joining two rigid structural members by means of a threaded fastener which is threaded into a plastic boss protruding outwardly from the surface of the first rigid structural member, the plastic boss being provided with a metal cup-shaped cap which grips the boss sufficiently to prevent the cap from rotating as the threaded fastener is being received through the cap and into the bore in the boss. The purpose of the metal cap is to prevent loosening of the fastener caused by cold flow of the plastic and to prevent cracking and/or fracture of the plastic.
The techniques disclosed in the prior art for joining a plastic member to another structural member by means of a double-ended fastener have not been totally satisfactory. The multiple step process of placing and securing the metal cup-shaped cap over the plastic bore, aligning the opening in the end wall of the cap with the bore in the boss and placing the threaded fastener into the hole in the cap as well as the handling of second small parts, namely the fastener and the metal cap, is considered cumbersome and disadvantageous.
Accordingly, the general object of the present invention is to provide a new and improved collar stud assembly which overcomes the disadvantages of the prior art practices.
More particularly it is an object of the invention to provide a collar stud assembly suitable for use in plastic wherein the double-ended fastener and metal cap may be pre-assembled as a unit and the cap always is in position to fit properly over the boss.
It is another object of the present invention to provide a pre-assembled collar stud unit which insures proper alignment of the fastener and hole in the metal cap with the bore in the plastic boss in a one step process and without the handling of a multiplicity of parts.
Other objects and advantages of the present invention will become apparent from the following discussion and from the drawings.
While the invention is susceptible of various modifications and alternative forms, there will be herein described in detail the preferred embodiments. It is to be understood, however, that it is not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended to cover modifications and alternative forms falling within the spirit and scope of the invention as expressed in the appended claims.